M88 is quarter panel stripe for a later 1970s models something, the guy must have used a generic online decoder. M88 on a 1970 Gran Coupe is different than on a Cuda, online decoders do not catch stuff like that.

The H in H6XW is the price class, High.

There is no way to know how many cars were made in any certain color with the VIN prefix.

I have started to track the colors in the 1970 Hamtramck & LA Registries, but I still have about 6000 car files to go back through & add that data to the databases.